Neoprene-polybutadiene freezeresistant composition



Patented July 1, 1950 NEOPRENE-POLYBUTADIENE FREEZE- RESISTANT COMPOSITION Delbert C..Cline, Silver Lake, Ohio, assignor to The Firestone Tire & Rubber Company, Akron, Ohio, a corporation of Ohio No Drawing. Application September 8, 1944, Serial No. 553,281

'4 Claims. (01. zen-41.5)

This invention relates to. improved soft vulcanized rubbery compositions.

Certain synthetic rubber-like materials have been found superior to natural rubber compositions for many specific uses. Among these rubber-like materials is neoprene, a synthetic rubber derived from the polymerization or copolymerization of chloroprene, a halogenated conjugated'diolefin, otherwise known as 2-chloro- 1,3-'-butadiene. occur in several variations wherein some par ticular quality is emphasized-in each species. The neoprenes are in general superior to natural rubber or its substitutes, when agingin sunlight is the primary concern. A typical example of rubber articles subject to the severe action of sunlight is the increasingly large number of rubber installations on exposed portions of aircraft. Many natural rubber installations of this type have failed prematurely in service because of the deteriorating effect of the sunlight thereon. Consequently, neoprene preparations have been used in deicers, fabric coatings on balloons, life boats, pontoons, and air spring bellows. Chloro- -prene polymers also possess excellent oil and heat resistance when compounded properly. They are, therefore, often a preferred material for the -fabrication of motor supports, hose, gaskets,

diaphragms, or other articles requiring rubberlike construction and commonly exposed to oil in motors, turbines, mobile equipment and the like. In these uses and many others, neoprene is also valuable for its flame resistance. It does not support combustion except in the presence of a decomposing or gasifying temperature. Fire hazard at its worst h'as'been considerably redliced in the operation of aircraft, tanks, military vehicles, and all types of auxiliary serving equipment for the same. Further safety through the uses of these chloroprene polymers or copolymers is derived from their impermeability to gases. They are readily utilized in the construction of gas containing paraphernalia, such as lighter-than-air aircraft, hoses, tank linings, and poisonous-gas resistant clothing.

The neoprenes, while possessing all of these qualities in addition to a tensile strength almost equal to natural rubber, are inferior to natural rubber and many of its substitutes in freeze resistance. Human mechanical activities are now The chloroprene polymers now being extended to the polar regions, the substratosphere and presently,- perhaps, to the stratosphere. The service limits, as to low temperature, of the rubber-like materials are rapidly being approached and in many instances exceeded. Most of the elastomers may be compounded with softeners and so achieve new low temperature service ranges, but as greater amounts of the softeners are used so are the physical properties of the elastomer lowered. For uses in which the strength or elongation must be preserved in the presence of low temperature, softeners, as they now exist, do not meet the growing need for elastomers, efficient in high altitude and polar environments.

It is an object of this invention to provide synthetic rubber compositions which have superior physical properties to other synthetic rubbers when compounded for use at subzero temperatures. Another object is to provide synthetic rubber compositions which are efficient as elastomers at temperatures below those in which present elastomers can function. It is an object also to achieve great freeze-resistance without the loss of desirable physical properties, such as have beenheretofore expended in compounding rubber-like materials for low temperatures. Other objects will become obvious as the invention is described.

The objects of the invention are achieved by mixing neoprene with polybutadiene. This new synthetic rubber composition is found to have superior tensile strength, elongation, and flexibility when compared with other elastomers of similar freeze resistance, such as Buna S, Buna N, rubber, or their blends. The freeze resistance of compositions including neoprene and polybutadiene may be varied according to design requirements. Since tensile and elongation are reduced somewhat by increasing the proportion of polybutadiene mixed with neoprene, preparation of these mixtures may be governed by the lowest temperatures anticipated for a particular use.

The unexpected feature of this invention arises out of the advantages obtained when polybutadiene is substituted for softeners or plasticizers used as brittle point depressants. The following four examples which are suitable as stocks for spreading on fabric, will illustrate the 3 utility of this invention when polybutadiene is used in place of Circo Light Oil, a naphthenic base petroleum product with an aniline point of approximately 160 F. and a Saybolt viscosity of 160 seconds at 100 F.

Freeze resistance has been determined and measured, in the development of this invention by observing the temperature at which brittleness occurred, as the sample was gradually refrigerated. Brittle points were determined in the standard Bell Telephone Laboratory brittleness tester which in principle involves suddenly bending a small slab of elastomer approximately thickthrough a 90 angle over a round rod submerged in a bath at controlled temperature.

Examples 1 to 4 are as follows:

advantages accruing from the substitution of polybutadiene for these softeners will be demonstrated.

Polybutadiene as used in this invention may be prepared in a manner similar to large scale Buna S polymerization. One hundred sixty parts of water are mixed with five parts of sodium oleate and 0.3 part potassium persulfate. With this solution are mixed 1.0 part dodecyl mercaptan and 100 parts 1,3 butadiene. These ingredients are polymerized under pressure in a closed, agitated vessel at 122 F. until 80% conversion of the 1,3 butadiene has occurred. whereupon, the emulsion containing the dispersed polybutadiene is dropped to a stripping tank, 2% phenyl-beta naphthylamine is added as a stabilizer, and the unpolymerized 1,3 butadine is removed by vacuum distillation. The latex may then be coagu- Example lated with a 4% aluminum sulfate solution. This coagulum after being dried will yield a value of 1 2 3 4 approximately 50 when tested on the Mooney plastometer. Plasticity values of the polymer, ffff ffff :36 g g 5' g? however, are not critical to the practice of this Pglybutadipne 10 120 invention. 55,; {1 50,195 L6 L6 & L6 Other examples illustrating the practice of this Zinc 0xide. 10.0 10.0 10.0 10.0 invention are as follows: fifggi gig 3 8 2:8 0 Examples 5 to 8 inclusive show variation in the Dibenzothiazyld 3.2 3.2 3.2 3.2 neoprene-polybutadiene ratio in compositions n s t: a suitable as a we trad swck- Phenyl-beta-naphthylamine 4.0 4.0 4.0 V 1.0

5000 500.0 500.0 500.0 Examples Brittle pointinF .-3s -'40 ---46 -so Tensile strength, lbs./sq.in 3,400 3,100 1,700 1,750 5 6 7 8 1 Allsamples were heat 85 Neoprene-butadieneratio 90 10 80/20 70 00 00/40 v These four formulas are identical except for Pigmm Pam Parts Parts PM the neoprene-plasticizer ratio. In the first ex- Neoprena, 300 320 280 240 ample, n0 plasticizer or polybutadiene has been gggg e 6 3 g 2 added and may therefore be considered the con- Zinc 5512;: I: 10.0. 1010 10.0 1010 9 for Examples 2, 3 and Exampleg and 3 fiiiieiiiiltrij -133: 12313 12313 12328 12313 show relative quantities of polybutadiene and n rid i m pants thylene Circo Light Oil respectively, to obtain an 8 F. g gggggrg gggi gf q g} g: gjg 2:: increase in freeze resistance. It should be ob- Light a ci magnesia-n -6 served also that there was a loss of tensile 15 gg gfigliilgggi g if, 13 13 strength of 300 and 1700 pounds per square inch for polybutadiene and Circo Light Oil, respec- 0 557'5 tively'. Examples 3 and 4 ofier an interesting il -l qn -g 3,075 2,625 1,800 1.500 comparison in that almost Similar tensile t fititi io ii111?m%i?@IIIII 2Z3 333. $23 333 strengths were obtained but in Example 4 where 50 Brittle P a -30 ratio of neoprene to polybutadiene was used, an increase in freeze resistance of more than five fold over the Circo Light Oil formula in Example 3 resulted. A further examination of Examples 1, 2, and 3 reveals that six times more Circo Light Oil than polybutadiene per unitweight of neoprene was needed to obtain an 8 1?. increase in freeze resistance and was accompanied by a great sacrifice of tensile strength where the former was used.

Polybutadiene may be substituted in neoprene compositions for other plasticizers known for their capacity to increase freeze resistance, such as the butyl esters of aliphatic acids. Invariably,

polybutadiene is found to give less diminution of Examples 9,- 10, 11, and 12 are identical with Examples 5, 6, 7, and 8, respectively except that P33 soft black has been substituted for Channel Black.

Examples Tensile. lbs/sq. in 2, 600 2, 350 1, 975 1, 500 Modulus at 200% elongation 525 425 400 350 Elongation in percent 680 600 550 480 Brittle point in "F --50 68 Examples Pigments Parts Parts Parts Parts Parts Neoprene 100 100 100 90 80 Dibutyl sebacate (liquid plasticiz 10 Dibutyl phthalate (liquid plasticizer) 10 Polybutadiene. 10 20 Piperidinium pentamethylene dithiocarbamate 0.16 0.16 0.16 0. 16 0.16 Phenyl-beta-naphthylamine 2. 2. 00 2. 00 2. 00 2.00 Stearic acid 3.00 3.00 8. 00 3.00 3.00 Dibenzothiazyl disulfide 0.13 0.13 0.13 0.13 0.13 Soit black (P33) 26. 00 26. 00 26. 00 26. 00 26.00 Light calcined magnesia 8.00 8.00 8.00 8.00 8.00 Zinc oxide 5.00 5.0 5.00 5.00 5. 00

Tensile in lbs/sq. in 2, 675 2, 450 2, 500 2, 700 2, 400 Modulus at 200% elongation l, 675 l, 100 1, 100 1, 850 l. 875 Elongation in per cent 670 650 660 560 500 Brittle point in F 40 ---45 45 50 -75 Examples 16 and 17 well illustrate the superiority of polybutadiene over two of the most efficient freeze resistant liquid plasticizers, as shown in Examples 14 and 15.

This formula may be considered applicable as a stock for coating fabrics for moisture and gas resistance.

Example Pigments Parts Parts Parts Parts Neoprene 400 360 320 280 Polybntadiene 4O 80 120 S 1.6 1.6 1.6 1.6 10. 0 10.0 10.0 10. 0 4. 0 4. 0 4. 0 4. 0 Carbon black 62. 9 62. 9 62. 9 62.9 Dibenzothiazyl disulfide- 3. 2 3. 2 3. 2 3. 2 Light calcined magnesia. 12. 8 12.8 12.8 12.8 Candelilla Wax 1. 1. 5 1. 5 1. 5 Phenylbeta-naphthylamiue 4. 0 4. 0 4. 0 4. 0

Brittle points in "F 40 51 70 85 The above samples, as all the previous samples, were found to be quite flexible to within 3 F. of their brittle points.

The examples herein described demonstrate clearly the advantages to be derived from this invention. It is shown that neoprene when mixed with polybutadiene, becomes freeze resistant without the corresponding loss of tensile strength and elongation that softeners or plasticizers produce, when used to obtain similar degrees of freeze resistance. As less polybutadiene is necessary to efiectuate freeze resistance than softeners used for that purpose, a further advantage is had where it is desired to exploit fully the oil, flame or heat resistance of neoprene in that the neoprene is not substantially diluted and its inherent advantages thus nullified. The examples also disclose that polybutadiene may be mixed with neoprene in all'proportions and in 6 all types of compounds in which neoprene is used and effectually subserve the objects of this invention.

What is claimed is:

1. A soft vulcanized rubbery composition flex ible at low temperatures containing 10 to 40 parts of rubbery polybutadiene prepared by polymerization to 80% conversion in aqueous emulsion at 122 F. and, respectively, 90 to 60 parts of rubbery polychloroprene.

2. A soft vulcanized rubbery composition flexible at low temperatures containing to parts of rubbery polychloroprene and, respectively, 30 to 20 parts of rubbery polybutadiene prepared by polymerization to 80% conversion in aqueous emulsion at 122 F.

3. A soft vulcanized rubbery composition flexible at low temperatures containing 10 to 40 parts of rubbery polybutadiene prepared by polymerization to 80% conversion in aqueous emulsion at 122 F., respectively to 60 parts of rubbery polychloroprene, and carbon black.

4. A method of making a vulcanized" neoprene article flexible at low temperatures, which includes mixing 90 to 60 parts of rubbery polychloroprene with respectively 10 to 40 parts of rubbery polybutadiene prepared by polymerization to 80% conversion in aqueous emulsion at 122 F., and vulcanizing the resulting mixture to produce a soft vulcanized rubbery composition.

DELBERT C. CLINE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,279,450 Diehl Apr. 14, 1942 2,381,267 Drake Aug. 7, 1945 2,427,192 Brovsky Sept. 9, 1947 FOREIGN PATENTS Number Country Date 492,998 Great Britain Sept. 30, 1938 705,104 Germany Apr. 17, 1941 OTHER REFERENCES Selker et a1: Pages 157-160, Ind. & Eng. Chem., Feb. 1942.

Conant et al.: Pages 767, 773, 774, Jour. of Applied Physics, Nov. 1944.

9Johnson: Page 1, column 1, Rubber Age, April 1 49.

lidska: Pages 40-46, Ind. and Eng. Chem., Jan. 19 4.

Scott: Pages 23-26, Feb. 1944, Jour. of Rubber Research of the Research Assn. of Br. Rub. Mfrs. Fraser et al.: The Neoprenes, pages 11, 12 and 13, Report No. 42-3, Sept. 1942, by Rubber Chem. Div. Du Pont, Wilmington, Del.

Neoprene Report BL-122 (4 pages), pub. Oct. 15, 1943, by Rubber Chem. Div. Du Pont.

Neoprene Report 31-149 (3 pages), pub. Mar. 25, 1944, vby Rubber Chem. Div. Du Pont. 

1. A SOFT VULCANIZED RUBBERY COMPOSITION FLEXIBLE AT LOW TEMPERATURES CONTAINING 10 TO 40 PARTS OF RUBBERY POLYBUTADIENE PREPARED BY POLYMERIZATION TO 80% CONVERSIN IN AQUEOUS EMULSION AT 122*F. AND, RESPECTIVELY, 90 TO 60 PARTS OF RUBBERY POLYCHLOROPRENE. 